You'll probably be familiar with the "Trinity shield", perhaps from a stained-glass window. It illustrates that while the Father is not the Son, the Son not the Spirit, and the Spirit not the Father, all three are still God

But did you know that it was quite probably invented by Robert Grosseteste (that man again!)? Richard Southern in his magisterial book on Robert Grosseteste points out that we find it for the first time in Durham Cathedral Library MS A.iii.12 fol.14v which is copied from Grosseteste's own notes.

Diagrams were important to Grosseteste. Whereas in the theological studies of the schools, texts were the raw material that needed to be analysed and explained, in his scientific studies the raw material was things, natural phenomena - and these were potentially of high theological significance too because it was understood that while humans signify through words, God could do so through things themselves.

Diagrams were a way both of representing the factual data and conveying its meaning more directly than a text could, and of making difficult concepts clear to a lay audience. For Grosseteste the preacher and Grosseteste the natural philosopher alike, they were part of how he thought, and how he communicated that thinking to his audiences.